RFR: 8264677 MemoryLeak: Progressindicator leaks, when treeShowing is false

[Florian Kirmaier]

Fixing leak in ProgressIndicator when treeShowing is false

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Commit messages:
 - 8264677

Changes: https://git.openjdk.java.net/jfx/pull/455/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=455&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264677
  Stats: 40 lines in 2 files changed: 39 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/455.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/455/head:pull/455

PR: https://git.openjdk.java.net/jfx/pull/455